A fuel cell (e.g., a polymer electrolyte fuel cell) is a device that causes a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air to electrochemically react with each other, to simultaneously produce electric power and heat. Since the fuel cell directly or indirectly converts the chemical energy of the fuel into electric energy, high power generation efficiency can be achieved.
The fuel cell is generally configured by: stacking a plurality of cells (unit cells); and fastening them with fastening members such as bolts under pressure. One cell is configured such that a membrane electrode assembly (hereinafter referred to as the MEA) is sandwiched by one paired plate-like conductive separators. The MEA has its peripheral portion (hereinafter also referred to as the outer circumferential region) retained by a frame member formed to be casing trim-like, for the purpose of improving handleability. It is noted that, as used herein, the MEA provided with the frame member is referred to as the electrode-membrane-frame assembly.
The MEA is configured by a polymer electrolyte membrane having its outer circumferential region (peripheral portion) retained by the frame member, and paired electrode layers that are respectively formed at the opposing faces of the electrolyte membrane and that are arranged on the inner side of the frame member. The paired electrode layers are configured by catalyst layers formed at the opposing faces of the polymer electrolyte membrane, and gas diffusion layers respectively formed on the catalyst layers. By the paired electrode layers being supplied with a reactant gas (fuel gas or oxidant gas), an electrochemical reaction occurs, whereby electric power and heat are produced.
Further, on the surface of the frame member, a gasket (elastic member) is provided so as to seal between each separator and the frame member, in order to block or suppress leakage of the reactant gas to the outside. The gasket is normally made of a resin material.
The gasket normally contains additives or softeners, which are required for retaining the gas leakage avoiding function. Further, the gasket normally contains plasticizers, additives, and antioxidants, which are required for forming the shape of the seal through injection molding or the like, and reactants thereof or degradation products remained after the molding. These substances contained in the gasket may include impurity which serves as a catalyst poison inhibiting the power generating reaction of the fuel cell. Accordingly, the conventional fuel cell configured as described above involves the problem that the impurity contained in the gasket is eluted into moisture in the reactant gas or into water produced in accordance with the electrochemical reaction, whereby the electrode layer is poisoned. When the electrode layer is poisoned, the electrochemical reaction is inhibited, and a reduction in the power generation performance of the fuel cell is invited.
Therefore, conventionally, a resin material (e.g., fluorine-base resin) from which impurity is not eluted or is eluted little is employed as the material of the gasket, or a structure with which the impurity eluted from the gasket does not poison MEA or poisons little MEA is employed.
For example, Patent Document 1 (JP 2009-170273 A) discloses a fuel cell in which a frame member is formed so as to cover the outer circumferential region of a gas diffusion layer. By allowing a projection provided at the frame member to penetrate through the gas diffusion layer to suppress shifting of the frame member, the necessity of providing the gasket is eliminated.
Further, Patent Document 2 (JP 2003-217613 A) discloses a fuel cell in which the impurity eluted from the resin material is adsorbed by an adsorptive medium dispersedly arranged in the separators or the gas diffusion layers, to thereby achieve purification.